FIG. 1 shows a standard configuration for enabling mobile communications between a Mobile Node MN, such as a portable telephone, and a corresponding node, not shown, via the Internet I. The Mobile Node MN is wirelessly connected to the network via the Access Points, AP1, AP2, AP3 etc and the Access Routers AR1, AR2 are connected to the Internet via a Router R.
Initially, with the Mobile Node MN in the position shown, signals are exchanged between the Mobile Node MN and the Internet via access point AP2, Access Router AR1 and Router R. When the Mobile Node is to be handed over from Access Point 2 to Access Point 3, for example because it is travelling from one towards the other, handover initiation and handover acknowledgement messages are exchanged between Access Routers AR1 and AR2. The message sent from the new Access Router AR2 to the old Access Router AR1 will include a new care of address (nCoA) to be used by the Mobile Node once it is under the control of Access Router AR2. This new address is then communicated back to the Mobile Node MN. At a specified time after this event, data packets intended for the Mobile Node MN are no longer sent from AR1 to AP2 but are instead “tunnelled” from AR1 to AR2 in preparation for the Mobile Node MN being handed over from AP2 to AP3. At this point it is necessary for packets to be buffered in AR2 pending handover of the MN from AP2 to AP3 i.e. layer 2 (L2) handover. Once layer 2 handover has been completed, signals are exchanged between the MN and the AR2 via the AP3 so that packets can be directed from AR2 to AP3 and then the MN. Finally, a binding update message BU is sent from the MN to the Router R. At this point the router knows that the MN is in communication with AR2 so that it can send packets direct to AR2 without tunnelling from AR1 to AR2.
In the above example, there is a single Router R dealing with all handover requests. This Router needs to store and keep updated the care of addresses used by the Mobile Nodes as they move from place to place. In practice, having only one Router R would require too much processing time to manage a large number of Mobile Nodes (MNs).
More recently, so-called “mobile anchor points” have been proposed. These are discussed in many documents including U.S. patent publication US 2001/0046223A1 (described here as mobility agents). A mobility agent or mobile anchor point can perform the functions of a home agent including maintaining a list which provides a mapping between a home address of a Mobile Node and its corresponding current care of address. Mobile anchor points may be included at different levels of the network hierarchy (tiered mobile anchor points) and this can reduce signalling delay when a Mobile Node changes point of attachment to the network.